The diversion of water from streams and rivers has been an integral part of the development of the industrial and agricultural economies of the Pacific Northwest and other regions. This diverted water has ground grain, generated electric energy, irrigated arid lands, and been used for municipal water supplies and industrial purposes. Typically, the diversions are not screened, resulting in the ready movement of fish from the source streams into diverted water flows and ultimately to their death. In the Pacific Northwest, unscreened water diversions, amongst other causes, have resulted in the extinction of steelhead and salmon from over 50% of their historic range and have dramatically reduced salmon populations in the few remaining rivers and streams that support salmon. In addition, several races of Pacific Northwest salmonid species have gone extinct and several others are now listed as threatened or endangered.
During the development of irrigation and hydroelectric facilities, efforts have been made to achieve screened water diversion apparatuses that separate fish and/or debris from the diverted water flow. Generally speaking, these devices have not worked well and for that reason they are rarely used even though required by law in some instances. For example, in its 1996 study of Pacific Northwest salmon, the National Research Council reported that fewer than 1,000 of the 55,000 water diversions in Oregon were screened, and 3,240 were listed as a high priority for screening.
Representative fish screen embodiments are shown in U.S. Pat. Nos. 3,938,340 and 4,064,048, issued to Downs and U.S. Pat. No. 4,740,105, issued to Wollander. A common feature of these devices is that the fish screens are arranged substantially vertically. A significant problem with vertically arranged screens is that they are easily fouled or clogged, resulting in burdensome cleaning schedules or elaborate cleaning equipment that is of questionable efficacy (see, for example, the '105 patent).
Other screen arrangements are discussed in U.S. Pat. Nos. 4,526,494 and 5,385,428 issued to Eicher and Taft, respectively. These arrangements each employ a submerged diagonally disposed screen that slopes upwardly in the downstream direction. The diagonal screen arrangement promotes rapid movement of water through the screen and, in principal, generates a shear force that pushes smolt up the screen to a bypass mechanism. The rapid movement of water through the screen, however, causes debris and fish (particularly juvenile salmonid species) to be driven into or accumulated at the screen, thus leading to fouling and fish loss. The screens of both the '494 and '428 patents are pivotally mounted for flushing this debris off the screens. In practice, the screens have also required additional cleaning and maintenance.
It should also be recognized that the devices of the '494 and '428 patents are for major hydroelectric installations which tend to pass large volumes of water and be much better capitalized than agricultural irrigation districts and the like. The devices of the '494 and '428 patents tend to be prohibitively expensive for low profit margin and non tax or rate payer supported installations such as agricultural fields and rural residential uses, etc.
U.S. Pat. No. 6,132,626 issued to Hart for a Liquid Filter teaches a filtration unit that back flushes a screening element when it becomes blinded by solid material. The device of the '626 patent does not provided unimpeded flow past the screen, but rather forces all flow through the screen, except when operating in back flush mode.
It should further be recognized that the above-described screened water diversions do not approximate natural conditions, and thus they increase both physical stress on fish and fish mortality. For example, the '340 and '048 patents use a mechanical scoop that collects fish and drops them into a return conduit, while the '105 patent uses fish traps and a tubal transport system. Similarly, the '494 and '428 patents teach submerged conduits that use high velocity water flow through a tilted screen to shear fish off towards a bypass conduit. The '626 patent teaches a closed chamber that traps or pins fish on a screen, subsequently opening a trap door when the movement of pinned fish or other debris is sufficient to prevent fluid passage and activate a release mechanism. These are all unnatural stream features and work against the genetic programming of fish, leading to increase stress, injury and mortality.
A need thus exists for a screened water diversion that safely and efficaciously maintains fish in the non-diverted flow. A need also exists for such a screen diversion that approximates natural conditions, is substantially non-fouling, and is easy-to-use and low cost to implement and maintain.
In addition, a need exists for such a screened water diversion that embodies one or more of the following aspects: eliminates risk of predation of fish, is not susceptible to a “dry-screen” condition, ensures adequate water depth for passage and greatly minimizes or eliminates risk of screen plugging from sediment, among other aspects.